INFICON MDC-360 Thin Film Deposition Controller - Manual (Page 121)

MDC-360 DEPOSITION CONTROLLER
10-1
10. THEORY OF OPER N
MEASUREMEN
C-360 uses a quartz crys s the basic transducing element. The quartz
lf is a flat circular plate approxim 0.55 in. (1.40 cm) in diameter
.013 in. (28-33mm) thick for 6 a Hz. ystal thickness is
roportional to the crys frequency. The crystal is excited into
y means of ternal ator. nloaded crystal
the thickness shear m t appr ly th ency of the
rystal. The frequency hich th z cry cillates is lowered
ion of material to its ce.
M THICKNESS CALCULATIO
estigators noted that if o assume aterial to the
e same effect as the addi f an e ass of quartz, the
d late the film thickness to the change in
frequency.
ency constant for an “ cut quartz crystal vibrating in thickness
8 x 10
5
Hz x cm.
ity of quartz g/cm
3
.
cy of unco crysta
ency of loade stal.
thickness.
y of film g/cm
3
.
quation proved to be adequ in most cases, however, note that the
roportionality is not actually co beca equation contains
uency which of co hang he fil s up. Because the
quency change wa l enough, the change in scale factor fell
ptable limits.
ATIO
10.1 BASIC T
The MD tal a
crystal itse ately
and 0.011-0 nd 5 M The cr
inversely p tal
mechanical motion b an ex oscill The u
vibrates in ode a oximate e frequ
specified c at w e quart stal os
by the addit surfa
10.2 FIL N
Early inv ne d that the addition of m
surface produced th tion o qual m
following equation could be use to re
crystal
where:
N
q
= Frequ AT”
shear (Hz x cm).
N
q
= 1.66
Dens
ρ
q
=
f
q
= Resonant frequen ated l.
f = Resonant frequ
d cry
Tk = Film
f
ρ
= Densit
f
This e
ate
constant of p nstant use the
the crystal freq urse c es as t m build
achievable fre s smal
within acce
THEORY OF OPERATION
(
f
)
f TK
N
f
q q
f
q
=
f
⋅
⋅
−
ρ
ρ
2
(1)